Sockeye salmon

Appearance

The sockeye salmon is sometimes called red or blueback salmon, due to its color. Sockeye are blue tinged with silver in color while living in the ocean. When they return to spawning grounds, their bodies become red and their heads turn green. Sockeye can be anywhere from 60 to 84 cm in length and weigh from 2.3 to 7 kg. Two distinguishing features are their long, serrated gill rakers that range from 30 to 40 in number, and their lack of a spot on their tail or back.

Naming

The sockeye salmon is the third-most common Pacific salmon species, after pink and chum salmon. "Oncorhynchus" comes from the Greek ὄγκος meaning "barb", and ῥύγχος meaning "snout". "Nerka" is the Russian name for the anadromous form. The name "sockeye" is an anglicization of "suk-kegh", its name in Halkomelem, the language of the indigenous people along the lower reaches of the Fraser River. "Suk-kegh" means "red fish".

Distribution

Some sockeye salmon populations are completely landlocked. Sockeye that live and reproduce in lakes are commonly called "kokanee", which is red-fish name in the Sinixt Interior Salish language and silver trout in the Okanagan language. They are much smaller than the anadromous variety and are rarely over 35 cm long. In the Okanagan Lake and many others, there are two kinds of kokanee populations – one spawns in streams and the other near lake shores. Landlocked populations occur in the Yukon Territory and British Columbia in Canada, as well as, in Alaska, Washington, Oregon, California, New York, Utah, Idaho, Montana, Nevada, Colorado, New Mexico, and Wyoming in the United States. Nantahala Lake is the only place in North Carolina where kokanee salmon are found. The fish, which is native to western North America, was stocked in Nantahala Lake in the mid-1960s by the NC Wildlife Resources Commission in an attempt to establish the species as a forage fish for other predator fishes in the lake. This stock has remained and become a favorite target for anglers.

In Japan, a landlocked variety termed black kokanee, or ""kunimasu"" in Japanese, was deemed to be extinct after 1940, when a hydroelectric project made its native lake in northern Akita Prefecture more acidic. The species seems to have been saved by transferring eggs to Saiko Lake, 500 kilometers to the south, however. This fish has been treated as a subspecies of sockeye "Oncorhynchus nerka kawamurae", or even an independent species "Oncorhynchus kawamurae".

Behavior

Sockeye salmon exhibit many different life histories with the majority being anadromous where the juvenile salmon migrate from freshwater lakes and streams to the ocean before returning as adults to their natal freshwater to spawn. Similar to most Pacific salmon, sockeye salmon are semelparous, meaning they die after spawning once. Some sockeye, called kokanee, do not migrate to the ocean and live their entire lives in freshwater lakes. The majority of sockeye spawn in rivers near lakes and juveniles will spend one to two years in the lake before migrating to the ocean, although some populations will migrate to saltwater in their first year. Adult sockeye will spend two to three years in the ocean before returning to freshwater. Females will spawn in 3–5 redds over a period of several days. The eggs usually hatch within six to nine weeks and the fry typically rear in lakes before migrating to the ocean.

Habitat

Sockeye salmon range as far south as the Columbia River in the eastern Pacific and in northern Hokkaidō Island in Japan in the western Pacific. They range as far north as the Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. The farthest inland sockeye salmon travel is to Redfish Lake, Idaho, over 1,400 km by river from the ocean and 2,000 m in elevation. In the United States, populations of sockeye salmon have been extirpated from Idaho and Oregon.

Reproduction

Males partake in competitive and sneaking tactics, formation of hierarchies, and non-hierarchical groupings around females who are ready to mate. Reproductive success varies more in males than females. The greater variability in male reproduction is associated with the greater average size and exaggerated shape of males. Reproductive success in females is determined by the number of eggs she lays, her body size, and the survival of the eggs, which is due in part to the quality of the nest environment. Male spatial distribution depends on shifts in reproductive opportunities, physical traits of breeding sites, as well as the operational sex ratio of the environment.

Non-dominant males adopt a subordinate behavior, acting as a satellite to mated pairs. During spawning, a subordinate male will move quickly into the redd and release their sperm. Nearby dominant males from other redds will also do this. Male social status is positively correlated to length and dorsal hump size. Larger females tend to spawn in shallower water, which is preferred over deeper water.

There is a dramatic sexual dimorphism at maturity. Males go through numerous morphological changes at maturation including, an increase in body depth, hump height, and snout length. Snout size also increases in females, but hump height and adipose fin length do not increase. This could mean that longer snout sizes are sexually selected, but hump height and adipose fin length are not. Females develop large gonads that are about 25% of the body mass.

Females are responsible for parental care. They select, prepare, and defend a nest site until they die or are displaced. Males do not participate in parental care at all, and they move between females after egg deposition.

Food

Sockeye salmon use patterns of limnetic feeding behavior, which encompasses vertical movement, schooling, diel feeding chronology, and zooplankton prey selectivity. They can change their position in the water column, timing and length of feeding, school formation, and choice of prey to minimize the likelihood of predation. This also ensures they still get at least the minimum amount of food necessary to survive. All of these behaviors contribute to the survivability, and therefore fitness of the salmon. Depending on location and threat of predation, the levels of aggressive feeding behavior can vary.

Sockeye salmon, unlike other species of Pacific salmon, feed extensively on zooplankton during both freshwater and saltwater life stages. They also tend to feed on small aquatic organisms such as shrimp. Insects are part of their diets at the juvenile stage.